1. Field of the Invention
The present invention relates to a semiconductor device and fuse blowout method. In particular, the present invention relates to a semiconductor device having a current blown fuse and a fuse blowout method.
2. Description of the Background Art
In a semiconductor device of a large capacity recently developed, it is technically difficult to fabricate all memory cells of a memory unit without problems to operate normally, and in the case where a failure memory cell is found in the fabrication stage, a memory array (column array, row array) having the failure memory cell is replaced with a spare memory array prepared in advance. For this purpose, redundant circuits of memory arrays in the number estimated from the rate of failure are prepared.
This prevents a semiconductor device itself from being a failure product and allows increase in a manufacturing yield of the semiconductor device.
The connection and disconnection between the memory array having a failure memory cell and the spare memory array are switched by a fuse. Generally, a column decoder and a row decoder of the peripheral circuits are configured so that the memory array having a failure memory cell cannot be selected while a spare memory can be selected by blowing the fuse.
The fuse blowout methods include a method using the laser beam and a method using electricity. The blowout method using the laser beam poses the problem that the fuse for the semiconductor device only in wafer form can be blown out and the process is complicated.
In the electrical blowout method, on the other hand, the fuse for the semiconductor can be blown out not only in wafer state but also after being packaged.
Further, the electrical blowout method is roughly divided into two categories.
One category is what is called the antifuse method using a fuse of a structure having electrodes arranged with an insulating film therebetween, in which the states of “0” and “1” are programmed by impressing the two electrodes with such a voltage as to cause the dielectric breakdown of the insulating film. The other method is a current blown fuse method using a fuse having the configuration of a conductive layer, which is programmed by blowing out the fuse with at least a rated current.
The current blown fuse is configured of a linear fuse portion actually blown out and fuse lead portions at the ends of the fuse portion. The fuse portion is designed to be thinner than the fuse lead portions. This is in order to increase the current density locally by efficient joule heat generation in the fuse portion and to facilitate the blowout of the fuse portion with a small current.
In this way, the current blown fuse is blown out utilizing the joule heat generation by the current supplied. The blowout of the fuse, therefore, requires a current of at least several tens of mA, which in turn requires a power supply having a large current output, and the effect that the heat generated by the fuse blowout has on the environment poses a problem.
In order to solve these problems, the reduction of the current required for fuse blowout is effective, and a fuse structure disclosed in Japanese Patent Application Laid-Open No. 06-140510 (1994), for example, has been proposed as a method to reduce the current.
Specifically, Japanese Patent Application Laid-Open No. 06-140510 (1994) discloses a technique in which the fuse portion assumes no simple linear form, but includes at least one crank portion at which the current is concentrated to increase the current density, so that the fuse is blown out with a small amount of current.
Japanese Utility Model Application Laid-Open No. 03-28737 (1991) (FIGS. 1, 2), on the other hand, discloses a structure in which the fuse portion is folded back with a plurality of turns into a meandering form to reduce the occupied area.
In Japanese Patent Application Laid-Open No. 06-140510 (1994), as shown in FIG. 2, the current density increases in the crank portion. In the other portions, however, the current density decreases and the effect of the current density increases in the crank position is offset. As compared with the linear fuse, therefore, no conspicuous effect is not expected.
In Japanese Utility Model Application Laid-Open No. 03-28737 (1991), on the other hand, the fuse assumes a meandering form to reduce the occupied area. The effect of reducing the blowout current, however, is not clear, and it is concluded that the blowout current is not reduced for not less than a predetermined length of the fuse portion. Therefore, the fuse structure is not considered to have been optimized.